d547f26c7d
While the mkdir option deals with the case where we don't want to clobber a mount point with directories (like ZFS, gluster or NFS), putting a directory storage directly onto a mount point is still risky: If the path exists - which it usually does even if not mounted - the storage will be considered successfully activated, but empty (or with unexpected content). Some operations will then lead to unexpected problems: the free_disk operation for instance only warns if the disk does not exist, but does not throw an error. In this case the configuration might be updated without the real disk being deleted. Once it's mounted back in, later operations which check existing disks which are not part of the current VM configuration (like migration) might error unexpectedly. This adds an 'is_mountpoint' option to directory storages which assumes the directory is an externally managed mount point (eg. fstab or zfs) and changes activate_storage() to throw an error if the path is not mounted.